The present invention is an improved leveling system for achieving and maintaining a desired, level position for a platform or structure. The predominant application of the present invention will be in recreational vehicles and motor coaches that are driven from place to place and parked for substantial periods of time on potentially uneven surfaces. However, other applicationsxe2x80x94including applications on generally fixed structures subject to vibration, tilting, or other disturbancesxe2x80x94will be understood to be encompassed by the presently claimed invention.
Leveling systems of various types for recreational vehicles are known in the art and have been sold for many years. Examples of such leveling systems may be found in U.S. Pat. Nos. 4,746,133, 4061,309, 4,165,861, 4,597,584, and 4,743,037. The ""584 and ""037 patents disclose an automatic leveling system including a fluid-based level sensor. The level sensor of the ""584 patent comprises a group of switches disposed in a plane. The switches of the ""584 patent comprise housings having a blob of mercury contained therein. The mercury is disposed within the housing with an open circuit that may be closed by the conductive mercury when a selected range of leveling positions cause the blob of mercury to move into position and serve as a bridge between the otherwise open circuit ends.
In the ""584 and ""037 patents, the switches are disposed to detect level disturbance individually for each wheel. The ""133 patent utilizes switches similar to those just described, but in a disposition that detects level disturbances at a shift of about 45degrees from the detection positions disclosed in the earlier patents. The ""133 patent allows control of leveling through actuation of paired jacks (rear, front, left, or right). In addition, the ""133 patent discloses the use of an air bag leveling system.
Notwithstanding these leveling systems, there has remained a need for an improved, dynamic level sensing and level adjustment control system to achieve and maintain a level structure efficiently, with a minimum of movement. There has further been a need for a level sensor that accommodates generally unavoidable conditions such as changes in the volume of a fluid sensor material associated with temperature changes, mechanical disturbances caused by passenger or occupant activity, or vibration caused by engines, drive systems or road conditions while the vehicle is in motion.
In addition to the circuit closing sensors of the type described, there are known fluid-based level sensors that depended on differential wetting of an electrode or terminal. In theory, the differential wetting allows determination of a fluid level and therefore plane orientation or tilt. However, such systems have inherent infirmities due to boundary layer effects, the interference of the probes, terminals, or electrodes with the movement of the fluid, or changes in fluid volume and viscosity due to temperature changes. For application in recreational vehicles where the vehicles may travel through regions of dramatically changing temperature extremes and experience motion due to moving passengers, correction of temperature change infirmities and the minimization of system response to minor vibrations are important considerations. Sealed biaxial inclinosensor technology utilizing conductometric measurement via thin film sensor substrates provides a convenient method to overcome these infirmities.
A technology has been developed by others and is employed within the method and system of the present invention. The technology relates to a biaxial inclinosensor such as the NS-25/B2 produced and marketed by HL-Planartechnik Gmbh, Hauert 13, D-44227, Dortmund, Germany, which is disclosed in U.S. Pat. No. 5,182,947. Such sensors employ a sealed chamber with a thin-film sensor substrate disposed on a portion of the bottom of the chamber. The sealed chamber is typically ceramic to provide for maximum durability across a wide variety of temperatures and conditions. The chamber is partially filled with an electroconductive fluid (the particular fluid and amount of fluid may vary from application to application depending on the range of measurements deemed to be consequential for the application). Voltage potential differences may be applied at locations on the sensor substrate along the chamber bottom wall and the resultant electrical field generated by the flow of current through the fluid and between the terminals may be detected at a selected location on the thin film sensor substrate. With this known technology, the level of fluid above a detection point may be determined.
The basic methodology of such biaxial inclinosensors and conductometric measurements are known and, as such, are not discussed at further length herein. FIGS. 1 and 2 (prior art) illustrate such a sealed-chamber, biaxial inclinosensor. FIG. 3 (prior art) illustrates a microprocessor and circuitry associated with such a sensor.
Notwithstanding this known art as illustrated in FIGS. 1-3, there has remained a need for a level detection and correction system and method that better accommodates disturbances in recreational vehicles created by vibration from engine operation, occupant movements, etc. It is therefore an object of the present invention to provide a system for level or level disturbance detection that overcomes the noise of vehicle or structure vibration. It is a further object of the present invention to provide a system for level correction that is integrated with the system for level detection. It is a further object of the present invention to provide such a system that may be used to level recreational vehicles with selected ranges of disturbance without taxing the leveling system drive components through constant response to minor disturbances that need no correction. It is a further object to provide such systems utilizing conductometric measurement principles.
The present invention is an improved, dynamic level detection and leveling system. A biaxial inclinosensor is used to generate a series of measurements that reflect a level of tilt associated with a plane that a user desires to maintain level. When sufficient measurements have been collected, an average value is obtained. If the average value obtained exceeds (in either direction, low or high) a selected value limit, then corrective action may be instituted, or a signal may be generated to indicate a need for automatic or manual correction. Such measurements are taken along both axes of the biaxial sensor.
It is preferred to minimize leveling system response by selecting not only a value limit, but also a null value limit. The value limit is used to determine an outside range of acceptable values for averaged measurements. When the value limit is exceeded, the corrective action is instituted, but since the values are averaged over a sampling of times it will not adjust the leveling for every slight and temporary change. Such corrective action would require almost continual adjustment of the hydraulic, pneumatic, electric, or other drive mechanisms used to adjust the level of the structure. Similarly, it is not sufficient to merely correct the imbalance or disturbance to a point just within the range defined by the value limits. Such a correction would often result in an almost immediate need for further correction. Therefore, there is also defined within the present invention a null range of value limitations to define an acceptable range of average values for the termination of corrective action, which range is within the broader range of values used to define the limits for when corrective action should be initiated.
By employing the biaxial inclinosensors having conductometric measurement capabilities, temperature induced fluid changes generally do not impact operation of the level detection system. Use of the thin-film sealed chamber technology eliminates or at least severely minimizes the interference of boundary layer effects with measurement and the interference of physical disturbance of fluid flow by probes that extend into the fluid""s path. Finally, the multiple-measurement, averaged value technique of the present invention eliminates constant system response, overcorrection, and over-active leveling system correction through the muting of minor, isolated disturbances, and through the establishment of a broad range of inclination angles that trigger the commencement of corrective action along with a narrower range of inclination angles that trigger the termination of such action.